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Quarterly Financial Data - Schedule of Quarterly Financial Information (Parenthetical) (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule Of Quarterly Financial Data [Line Items]
Gross profit (loss)	$ (10,204)	$ (7,285)	$ 11,340	$ 11,615	$ (8,892)	$ (36,379)	$ 2,129	$ (6,164)	$ 5,466	$ (49,306)	$ 20,048
Loss from continuing operations	(162)	(17,112)	(7,033)	(5,986)	(25,190)	(39,490)	(7,688)	(15,765)	$ (30,293)	$ (88,133)	$ (46,146)
Interest Expense [Member]
Schedule Of Quarterly Financial Data [Line Items]
Loss from continuing operations	9,326	9,291	9,292	9,358	9,816	13,333	6,446	1,350
Benefit for Income Taxes [Member]
Schedule Of Quarterly Financial Data [Line Items]
Loss from continuing operations	(30,018)	(6,698)	(2,761)	(1,282)
Impairment of Goodwill [Member]
Schedule Of Quarterly Financial Data [Line Items]
Loss from continuing operations					1,621
Depreciation Expense [Member]
Schedule Of Quarterly Financial Data [Line Items]
Gross profit (loss)	(16,655)	(16,179)	(17,047)	(17,115)	(17,874)	(16,862)	(14,028)	(10,590)
Loss from continuing operations	$ (16,655)	(16,179)	(17,047)	$ (17,115)	$ (17,874)	(16,862)	(14,028)	(10,590)
Recovery of Precious Metals [Member]
Schedule Of Quarterly Financial Data [Line Items]
Gross profit (loss)			2,905
Loss from continuing operations			$ 2,905
Turnaround Costs [Member]
Schedule Of Quarterly Financial Data [Line Items]
Gross profit (loss)		(1,098)				(8,597)	(535)
Loss from continuing operations		$ (1,098)				$ (8,597)	$ (535)
Consulting Fee - Property Tax Services [Member]
Schedule Of Quarterly Financial Data [Line Items]
Gross profit (loss)								(12,095)
Loss from continuing operations								$ (12,095)